A driving method using an inverter has been employed to control driving of an alternating-current motor using a direct-current power source. The inverter is controlled for switching by an inverter driving circuit. For example, the alternating-current motor is fed with a voltage switched in accordance with PWM control.
Further, Japanese Patent Laying-Open No. 2008-11682 (Patent Document 1) discloses a PWM control configuration for control of driving of such an alternating-current motor. In current feedback control for compensating a deviation of a d deviation axis current and a deviation of a q axis current, the PWM control configuration selectively applies sinusoidal wave PWM control (FIG. 2 of Patent Document 1) and overmodulation PWM control (FIG. 3 of Patent Document 1). In the sinusoidal wave PWM control, the amplitude of a voltage command is not more than the amplitude of a reference triangular wave, whereas in the overmodulation PWM control, the amplitude of the voltage command exceeds the peak value of the reference triangular wave.
In particular, in Patent Document 1, for the control for the alternating-current motor, rectangular wave control is further applied. In the rectangular wave control, the alternating-current motor is fed with a rectangular wave voltage having a voltage phase controlled in accordance with a torque deviation. Also described therein is an art for stabilizing the switching of control modes between the rectangular wave control and the overmodulation PWM control.